Many proposals have been made and known for a solid catalyst component comprising a titanium halide compound, a magnesium compound and an electron donor compound as essential components and a process for the polymerization of olefins in the presence of a catalyst comprising said solid catalyst component, an organic aluminum compound and a third component such as a silicon compound.
Further, a solid catalyst component prepared from a dialkoxymagnesium and titanium tetrachloride as main starting materials and a catalyst for polymerization of olefins made of said solid catalyst component, an organic aluminum compound and a third component such as a silicon compound have been known as disclosed in JP-A-63-3010 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-1-221405, JP-A-1-315406, JP-A-3-227309, JP-A-3-70711, JP-A-4-8709, and many other references.
The foregoing various techniques focus on the development of a catalyst component which is active enough to allow the omission of a so-called deashing step, i.e., step of removing catalyst residues such as chlorine and titanium remaining in the polymer produced by the polymerization of propylene in the presence of a catalyst as well as on the enhancement of the yield of stereoregular polymer. These techniques can provide excellent results on these purposes.
However, if a polymerization catalyst having a composition comprising this kind of a high activity type catalyst component, an organic aluminum compound and an electron donor compound such as silicon compound is employed to polymerize olefins, the polymer thus produced contains much fine powder derived from fine solid catalyst component itself or obtained by fragmentation due to reaction heat during polymerization. Thus, the polymer has a broad particle size distribution. As a result, the bulk density of the polymer thus produced tends to drop. If the content of the fine polymer is raised, the continuance of uniform reaction can be inhibited. Further, the pipe in the polymerization process can be blocked. Moreover, some troubles can occur at the separation step and the drying step of the polymer thus produced. It has been desired to solve these problems. In addition, if the particle size distribution is widened, it eventually gives undesirable effects on the formation of the polymer. If the bulk density of the polymer thus produced is lowered, the resulting productivity is extremely lowered. This is the reason why a polymer having as small fine polymer content as possible and a high bulk density has been desired.
In order to solve these problems, many methods have been proposed and are known for polymerizing olefins in the presence of a solid catalyst component comprising as essential components a magnesium compound such as dihalogenated magnesium and alkylmagnesium compounds, a titanium compound, an electron donor compound and a polysiloxane or a catalyst comprising said solid catalyst component, an organic aluminum compound and a third component such as a silicon compound. For example, JP-A-61-204202 discloses a catalyst component for polymerization of olefins prepared by allowing the reaction product of dihalogenated magnesium, titanium tetraalkoxide and hydrogenated polysiloxane, an acid halide compound and a silicon halide compound to come in contact with one another. Further, JP-A56-152811 discloses a process for the production of a polyolefin which comprises the polymerization of olefins in the presence of a catalyst comprising in combination a titanium-containing solid catalyst component derived from an alkylmagnesium compound, a polysiloxane, an organic acid ester and a titanium compound and an organic metal compound.
On the other hand, JP-A-6-157659 proposes a catalyst for polymerization of olefins made of a solid catalyst component obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixed solution of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, and then reacting the reaction product with titanium tetrachloride.
Further, JP-A-6-287225 proposes a solid catalyst component for polymerization of olefins obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixed solution of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, washing the reaction product with an aromatic hydrocarbon, and then again reacting the reaction product with titanium tetrachloride to obtain a solid component which is then dried and freed of fine powder.
Further, JP-A-6-287217 proposes a solid catalyst component for polymerization of olefins obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixed solution of an aromatic hydrocarbon and titanium tetrachloride-so that they are reacted, washing the reaction product with an aromatic hydrocarbon, again reacting the reaction product with titanium tetrachloride, drying the solid component thus obtained, removing fine powder from the solid component, and then adding a powdered nonionic surface active agent to the solid component.
The foregoing technique can remove the fine powder derived from the solid catalyst component itself, eventually exerting an effect of reducing the content of fine powder in the polymer thus produced. However, the effect of the foregoing technique does not go so far as to control the generation of fine powder due to fragmentation of particles by the reaction heat during polymerization, in particular in the initial stage of the polymerization reaction. Thus, a fine powder is still present in the polymer thus produced.
Further, the polymer produced according to the foregoing technique has a good morphology but has a low bulk density. In the production of a polyolefin, the amount of a polymer to be produced per unit volume in the polymerization tank is reduced, and the amount of the polymer to be processed during transportation or pelletizing step is limited. As a result, such a problem that the productivity throughout the entire process for the production of polyolefin is reduced is left unsolved. Further, even if a polymer having a relatively high bulk density can be obtained, the problem of drop of polymerization activity or stereoregularity is left unsolved.
From the standpoint of energy saving or conservation of resources related to the recent global environmental issue, it has been keenly desired to reduce the weight of plastics for use in automobile, household appliance, etc. In order to solve this problem, the thickness of molded plastic articles needs to be reduced while maintaining its strength such as impact strength. To this end, it is desired to further enhance the stereoregularity or crystallinity and hence the rigidity of the resin to be used. Accordingly, it has been desired to develop a catalyst for the production of a polyolefin which can provide a polymer having an enhanced stereoregularity or crystallinity.
On the other hand, a process for the production of a block copolymer of propylene has been known which comprises producing a crystalline polymer of propylene alone in the presence of a solid catalyst component or catalyst of the various conventional types at a first stage, and then copolymerizing propylene with another olefin such as ethylene and 1-butene in the copresence of said propylene homopolymer at a second stage.
Such a block copolymer contains a rubber-like copolymer in a certain proportion and thus exhibits an enhanced impact strength while maintaining an excellent rigidity characteristic of crystalline polypropylene. Therefore, such a block copolymer has found wide application, e.g., to container, automobile parts such as bumper and film requiring low temperature heat sealability.
In order to further enhance the impact strength of such a block copolymer, the proportion of a rubber-like copolymer (e.g., ethylene-propylene rubber) to be produced in the block copolymer needs to be raised. However, as the production ratio of rubber-like copolymer increases, the adhesion of the particulate block copolymer thus produced increases. As a result, the flowability of the particulate polymer thus produced shows a remarkable deterioration in the gas phase polymerization process or bulk polymerization process. Further, the polymer particles stick to each other to agglomerate or stick to the inner wall of the polymerization apparatus, causing serious troubles in the process operation.
For the purpose of eliminating the deterioration of the flowability of the particulate block copolymer or the adhesion of the particles causing agglomeration or the adhesion of the particles to the inner wall of the apparatus, JP-A-61-69821 and JP-A-61-69822 propose the supply of an active hydrogen compound such as ethanol or an oxygen-containing compound such as oxygen gas into the polymerization system at the second stage, i.e., stage of producing a rubber-like copolymer. However, such an active hydrogen compound or oxygen-containing compound originally causes deterioration of the activity of the catalyst in the polymerization of olefins. In this process, the amount of such an active hydrogen compound or oxygen-containing compound to be supplied needs to be closely controlled. Further, the apparatus to be used for this process needs to be improved.
The present invention is intended to solve the foregoing problems of the prior art techniques. In other words, an object of the present invention is to provide a solid catalyst component and catalyst for polymerization of olefins which can provide a polymer having a high bulk density and a small content of fine powder while maintaining the desired high polymerization activity and high yield of a high stereoregularity polymer. Another object of the present invention is to provide a solid catalyst component and catalyst for polymerization of olefins which can maintain its good particle properties even if the production ratio of rubber-like copolymer is raised in block copolymerization.